APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

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APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by APOD Robot » Wed Apr 04, 2018 4:09 am

Image Intrepid Crater on Mars from Opportunity

Explanation: The robotic rover Opportunity sometimes passes small craters on Mars. Pictured here in 2010 is Intrepid Crater, a 20-meter across impact basin slightly larger than Nereus Crater that Opportunity had chanced across previously. The featured image is in approximately true color but horizontally compressed to accommodate a wide angle panorama. Intrepid Crater was named after the lunar module Intrepid that carried Apollo 12 astronauts to Earth's Moon 49 years ago. Beyond Intrepid Crater and past long patches of rusty Martian desert lie peaks from the rim of large Endeavour Crater, visible on the horizon. The Opportunity rover continues to explore Mars, recently surpassing 5,000 Martian days on the red planet.

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RocketRon

Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by RocketRon » Wed Apr 04, 2018 5:22 am

What a neat punchy little crater.

How much harder do meteorites strike the surface of Mars because of its thin atmosphere,
compared to say on Earth. Anyone done the calcs, size for size ?

Also, wouldn't Mars' famous dust storms tend to fill in such things ?
What sort of time frame for it to more or less disappear, not ignoring that the crater walls are higher than its surroundings.

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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by Boomer12k » Wed Apr 04, 2018 8:51 am

Awesome... the "Little Rover that COULD".... "I think I can, I think I can, I think I can..."

Intrepid, indeed...

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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by heehaw » Wed Apr 04, 2018 9:21 am

"approximately true color." A nasty color!

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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by orin stepanek » Wed Apr 04, 2018 10:57 am

A lot of iron?
Orin

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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by Sa Ji Tario » Wed Apr 04, 2018 11:17 am

It is logical to think that the dust dragged by the winds would fill the impact craters, but with the speed in which these winds move through the profiles of the walls they would make a vacuum that will clean their bottom

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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by neufer » Wed Apr 04, 2018 2:29 pm

RocketRon wrote:
Wed Apr 04, 2018 5:22 am

What a neat punchy little crater.
Note that the picture is horizontally compressed.

Intrepid Crater is much like Eagle crater into which Opportunity first came to rest:
https://en.wikipedia.org/wiki/Eagle_(Meridiani_Planum_crater) wrote: .
<<Eagle is a 22-metre long impact crater located on the Meridiani Planum extraterrestrial plain, situated within the Margaritifer Sinus quadrangle (MC-19) portion of the planet Mars. The Opportunity rover came to rest inside Eagle crater when it landed in 2004. Scientists were delighted that the rover landed there, as the crater contains rocky outcroppings that helped prove that Meridiani was once an ocean floor.

The name is a triple reference: in honor of the first manned spacecraft to land on the Moon in 1969; in honor of the launching country, the United States, whose symbol is an eagle; and in reference to the golf term eagle, referring to sinking a ball two strokes under par. The third reference extended the golf metaphor begun with a description of landing in the crater as "a hole in one".>>
RocketRon wrote:
Wed Apr 04, 2018 5:22 am

How much harder do meteorites strike the surface of Mars because of its thin atmosphere,
compared to say on Earth. Anyone done the calcs, size for size ?
Mars is orbiting somewhat slower than the Earth (24 vs 30 km/s) and its escape velocity is somewhat less (5 vs 11 km/s).

That being said, Mars's atmospheric density is only ~ 0.6% that of Earth and meter wide meteors that would break apart in Earth's upper stratosphere (resulting in subsonic meteorites falling on the ground) would easily make it intact to the surface of Mars at hypersonic velocities.

Using the rule of thumb that craters are about ten times larger than their hypersonic meteors:
Intrepid & Eagle were probably produced by hypersonic meteors about 2 meters in diameter.
RocketRon wrote:
Wed Apr 04, 2018 5:22 am

Also, wouldn't Mars' famous dust storms tend to fill in such things ?

What sort of time frame for it to more or less disappear, not ignoring that the crater walls are higher than its surroundings.
Shallow craters probably lose about as much dust as they collect (much like Opportunity's solar panels).
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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by Chris Peterson » Wed Apr 04, 2018 3:38 pm

RocketRon wrote:
Wed Apr 04, 2018 5:22 am
How much harder do meteorites strike the surface of Mars because of its thin atmosphere,
compared to say on Earth. Anyone done the calcs, size for size ?
Ordinary meteorites (that is, rocks the size of gravel to boulders) fall somewhat faster than they do on Earth because Mars's thin atmosphere results in a higher terminal velocity. But these are still subsonic, non-crater forming impacts. The survival rate may be somewhat higher on Mars because of the thinner atmosphere, but probably not by much. Most bodies still burn up in the atmosphere, just like here on Earth.

Large bodies that retain a fraction of their initial velocity and which cause craters are largely unaffected by the atmosphere (true on Earth, as well). Mars has a lower gravitational potential, which means it's possible for lower speed impacts than on Earth, which means there will be a shift in crater distribution towards smaller ones than are possible on Earth.
Chris

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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by neufer » Wed Apr 04, 2018 4:27 pm

Chris Peterson wrote:
Wed Apr 04, 2018 3:38 pm
RocketRon wrote:
Wed Apr 04, 2018 5:22 am

How much harder do meteorites strike the surface of Mars because of its thin atmosphere,
compared to say on Earth. Anyone done the calcs, size for size ?
Ordinary meteorites (that is, rocks the size of gravel to boulders) fall somewhat faster than they do on Earth because Mars's thin atmosphere results in a higher terminal velocity. But these are still subsonic, non-crater forming impacts. The survival rate may be somewhat higher on Mars because of the thinner atmosphere, but probably not by much. Most bodies still burn up in the atmosphere, just like here on Earth.
Not quite sure what you mean by "boulders."

The well documented 4-meter 2008 TC3 stony meteor exploded at an estimated altitude of 37 kilometers where the pressure is ~4.2 mb.

A smaller (2-meter diameter) slower iron meteor would surely make it all the way to the ~6 mb Martian surface to create a ~20 meter crater.
https://en.wikipedia.org/wiki/2008_TC3 wrote: <<2008 TC3 was an 80-metric-ton, 4.1-meter diameter asteroid that entered Earth's atmosphere on October 7, 2008. It exploded at an estimated 37 kilometers above the Nubian Desert in Sudan. Some 600 meteorites, weighing a total of 10.5 kilograms, were recovered; many of these belonged to a rare type known as ureilites, which contain, among other minerals, nanodiamonds. It was the first time that an asteroid impact had been predicted prior to its entry into the atmosphere as a meteor.

The meteor entered Earth's atmosphere above northern Sudan at 02:46 UTC (05:46 local time) on October 7, 2008 with a velocity of 12.8 km/s at an azimuth of 281 degrees and an altitude angle of 19 degrees to the local horizon. It exploded tens of kilometers above the ground with the energy of 0.9 to 2.1 kilotons of TNT over a remote area of the Nubian Desert, causing a large fireball or bolide.

The Times reported that the meteor's "light was so intense that it lit up the sky like a full moon and an airliner 1,400 km away reported seeing the bright flash." A low-resolution image of the explosion was captured by the weather satellite Meteosat 8. The Meteosat images place the fireball at 21.00°N 32.15°E. Infrasound detector arrays in Kenya also detected a sound wave from the direction of the expected impact corresponding to energy of 1.1 to 2.1 kilotons of TNT. Asteroids of this size hit Earth about two or three times a year.>>
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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by Chris Peterson » Wed Apr 04, 2018 4:48 pm

neufer wrote:
Wed Apr 04, 2018 4:27 pm
Chris Peterson wrote:
Wed Apr 04, 2018 3:38 pm
RocketRon wrote:
Wed Apr 04, 2018 5:22 am

How much harder do meteorites strike the surface of Mars because of its thin atmosphere,
compared to say on Earth. Anyone done the calcs, size for size ?
Ordinary meteorites (that is, rocks the size of gravel to boulders) fall somewhat faster than they do on Earth because Mars's thin atmosphere results in a higher terminal velocity. But these are still subsonic, non-crater forming impacts. The survival rate may be somewhat higher on Mars because of the thinner atmosphere, but probably not by much. Most bodies still burn up in the atmosphere, just like here on Earth.
Not quite sure what you mean by "boulders."

The well documented 4-meter 2008 TC3 stony meteor exploded at an estimated altitude of 37 kilometers where the pressure is ~4.2 mb.

A smaller (2-meter diameter) slower iron meteor would surely make it all the way to the ~6 mb Martian surface to create a ~20 meter crater.
These terms are useful as general indicators. The situation in reality is much more complex given issues such as shape and material strength and speed and impact angle. (Whether a 2m iron meteorite would arrive at the surface of Mars carrying a hypersonic speed is uncertain. If it were a 2m object before it encountered Mars, it would probably lose more than 90% of its mass to atmospheric ablation and simply drop non-cratering meteorites. If its original size was such that it was still 2m across at impact, it would likely be carrying some of its original speed, and therefore be capable of producing a small crater.)
Chris

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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by neufer » Wed Apr 04, 2018 6:23 pm

Chris Peterson wrote:
Wed Apr 04, 2018 4:48 pm
neufer wrote:
Wed Apr 04, 2018 4:27 pm
Chris Peterson wrote:
Wed Apr 04, 2018 3:38 pm

Ordinary meteorites (that is, rocks the size of gravel to boulders) fall somewhat faster than they do on Earth because Mars's thin atmosphere results in a higher terminal velocity. But these are still subsonic, non-crater forming impacts. The survival rate may be somewhat higher on Mars because of the thinner atmosphere, but probably not by much. Most bodies still burn up in the atmosphere, just like here on Earth.
Not quite sure what you mean by "boulders."

The well documented 4-meter 2008 TC3 stony meteor exploded at an estimated altitude of 37 kilometers where the pressure is ~4.2 mb.

A smaller (2-meter diameter) slower iron meteor would surely make it all the way to the ~6 mb Martian surface to create a ~20 meter crater.
These terms are useful as general indicators. The situation in reality is much more complex given issues such as shape and material strength and speed and impact angle. (Whether a 2m iron meteorite would arrive at the surface of Mars carrying a hypersonic speed is uncertain. If it were a 2m object before it encountered Mars, it would probably lose more than 90% of its mass to atmospheric ablation and simply drop non-cratering meteorites. If its original size was such that it was still 2m across at impact, it would likely be carrying some of its original speed, and therefore be capable of producing a small crater.)
I don't think that a 50 ton iron meteor pushing aside a few tons of Martian atmosphere is going to suffer that much in the way of ablation or speed loss.
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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by Chris Peterson » Wed Apr 04, 2018 6:31 pm

neufer wrote:
Wed Apr 04, 2018 6:23 pm
Chris Peterson wrote:
Wed Apr 04, 2018 4:48 pm
neufer wrote:
Wed Apr 04, 2018 4:27 pm

Not quite sure what you mean by "boulders."

The well documented 4-meter 2008 TC3 stony meteor exploded at an estimated altitude of 37 kilometers where the pressure is ~4.2 mb.

A smaller (2-meter diameter) slower iron meteor would surely make it all the way to the ~6 mb Martian surface to create a ~20 meter crater.
These terms are useful as general indicators. The situation in reality is much more complex given issues such as shape and material strength and speed and impact angle. (Whether a 2m iron meteorite would arrive at the surface of Mars carrying a hypersonic speed is uncertain. If it were a 2m object before it encountered Mars, it would probably lose more than 90% of its mass to atmospheric ablation and simply drop non-cratering meteorites. If its original size was such that it was still 2m across at impact, it would likely be carrying some of its original speed, and therefore be capable of producing a small crater.)
I don't think that a 50 ton iron meteor pushing aside a few tons of Martian atmosphere is going to suffer that much in the way of ablation or speed loss.
The characteristics of ablation in the Martian and Earth atmospheres are remarkably similar. This is related to the scale height of each. Most meteoroids that encounter the Earth burn up entirely while they're still above 100 km, at an atmospheric density similar to the Martian upper atmosphere. The most significant difference between the two planets when it comes to meteorite survival is the difference in gravitational potential.
Chris

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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by neufer » Wed Apr 04, 2018 7:26 pm

Chris Peterson wrote:
Wed Apr 04, 2018 6:31 pm
neufer wrote:
Wed Apr 04, 2018 6:23 pm
Chris Peterson wrote:
Wed Apr 04, 2018 4:48 pm

The situation in reality is much more complex given issues such as shape and material strength and speed and impact angle. (Whether a 2m iron meteorite would arrive at the surface of Mars carrying a hypersonic speed is uncertain. If it were a 2m object before it encountered Mars, it would probably lose more than 90% of its mass to atmospheric ablation and simply drop non-cratering meteorites. If its original size was such that it was still 2m across at impact, it would likely be carrying some of its original speed, and therefore be capable of producing a small crater.)
I don't think that a 50 ton iron meteor pushing aside a few tons of Martian atmosphere is going to suffer that much in the way of ablation or speed loss.
The characteristics of ablation in the Martian and Earth atmospheres are remarkably similar. This is related to the scale height of each. Most meteoroids that encounter the Earth burn up entirely while they're still above 100 km, at an atmospheric density similar to the Martian upper atmosphere. The most significant difference between the two planets when it comes to meteorite survival is the difference in gravitational potential.
The most significant difference between the two planets when it comes to meteorite survival is the fact that meteors like Hoba have to plow through ~60 times as much atmospheric mass in order to reach the surface of the Earth.
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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by MarkBour » Wed Apr 04, 2018 8:54 pm

So I'm an intrepid adventurer, and I go to live on Mars in the year 2040, one of the first groups to do so. After about 6 years, I find that I have grown sick of living indoors and of looking out my window at the never-much-changing red dirt landscape outside. :-(

Now what to do? I can't move back to Poughkeepsie ...
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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by Chris Peterson » Wed Apr 04, 2018 11:05 pm

neufer wrote:
Wed Apr 04, 2018 7:26 pm
Chris Peterson wrote:
Wed Apr 04, 2018 6:31 pm
neufer wrote:
Wed Apr 04, 2018 6:23 pm

I don't think that a 50 ton iron meteor pushing aside a few tons of Martian atmosphere is going to suffer that much in the way of ablation or speed loss.
The characteristics of ablation in the Martian and Earth atmospheres are remarkably similar. This is related to the scale height of each. Most meteoroids that encounter the Earth burn up entirely while they're still above 100 km, at an atmospheric density similar to the Martian upper atmosphere. The most significant difference between the two planets when it comes to meteorite survival is the difference in gravitational potential.
The most significant difference between the two planets when it comes to meteorite survival is the fact that meteors like Hoba have to plow through ~60 times as much atmospheric mass in order to reach the surface of the Earth.
Hoba is extremely unusual, not at all typical of meteorites. No, the mass of atmosphere is not all that significant when comparing Mars and Earth. As noted, the vast majority of meteoroids burn up high in either atmosphere, and the vast majority of large bodies (~10m+) make it to the ground in either case with hypersonic velocity and crater production. It is only a small number of intermediate size, or which have unusual speeds or impact angles, which will behave very differently.
Chris

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Re: APOD: Intrepid Crater on Mars from Opportunity (2018 Apr 04)

Post by neufer » Thu Apr 05, 2018 1:41 am

Chris Peterson wrote:
Wed Apr 04, 2018 11:05 pm
neufer wrote:
Wed Apr 04, 2018 7:26 pm
Chris Peterson wrote:
Wed Apr 04, 2018 6:31 pm

The characteristics of ablation in the Martian and Earth atmospheres are remarkably similar. This is related to the scale height of each. Most meteoroids that encounter the Earth burn up entirely while they're still above 100 km, at an atmospheric density similar to the Martian upper atmosphere. The most significant difference between the two planets when it comes to meteorite survival is the difference in gravitational potential.
The most significant difference between the two planets when it comes to meteorite survival is the fact that meteors like Hoba have to plow through ~60 times as much atmospheric mass in order to reach the surface of the Earth.
Hoba is extremely unusual, not at all typical of meteorites. No, the mass of atmosphere is not all that significant when comparing Mars and Earth. As noted, the vast majority of meteoroids burn up high in either atmosphere, and the vast majority of large bodies (~10m+) make it to the ground in either case with hypersonic velocity and crater production. It is only a small number of intermediate size, or which have unusual speeds or impact angles, which will behave very differently.
Right...intermediate size like say 2 meters across for iron (or perhaps 5 meters for stone).
Art Neuendorffer